Influencing factors of good quality of life among chronic obstructive pulmonary disease patients living in Zhejiang Province, China

Chronic obstructive pulmonary disease (COPD) is a chronic, progressive and debilitating disease that affects quality of life (QOL), especially among patients living in poor environments. This study aimed to determine the influencing factors of good QOL among COPD patients living in Zhejiang, China. A cross-sectional study was conducted to collect data from participants in six tertiary hospitals in Zhejiang Province by a simple random sampling method. A validated questionnaire was used to collect general information, environmental factors, and COPD stage. The standardized St. George's Respiratory Questionnaire (SGRQ) was used to assess QOL. Logistic regression was used to determine influencing factors of good QOL among COPD patients at a significance level of α = 0.05. A total of 420 participants were recruited for analysis. The overall prevalence of patients with good QOL was 25.7%. Six variables were found to be associated with good QOL in the multivariable analysis. Patients who were employed had 2.35 times (95% CI 1.03–5.34) greater odds of having good QOL than those who were unemployed. Those whose family income was higher than 100,000 CNY had 2.49 times (95% CI 1.15–5.39) greater odds of having good QOL than those whose family income was lower than 100,000 CNY. Those who had treatment expenses less than 5,000 CNY had 4.57 (95% CI 1.57–13.30) times greater odds of having good QOL than those who had treatment expenses of 5,000 CNY or higher. Those who had mild or moderate airflow limitation were 5.27 times (95% CI 1.61–17.26) more likely to have good QOL than those who were in a severe or very severe stage of COPD. Those who had a duration of illness less than 60 months had 5.57 times (95% CI 1.40–22.12) greater odds of having good QOL than those who had a duration of illness of 120 months or more. Those who were not hospitalized within the past 3 months had 9.39 times (95% CI 1.62–54.43) greater odds of having good QOL than those who were hospitalized more than twice over the past 3 months. Socioeconomic status, disease stage and accessibility were associated with good QOL among COPD patients in Zhejiang Province, China. Increasing family income and implementing measures to improve the accessibility of medical care, including developing a proper system to decrease the cost of treatment for COPD patients, can improve patients’ QOL.


Study population and study sample
The study population was COPD patients who attended one of six hospitals in Zhejiang Province, China.The inclusion criteria were those aged 40 years and over and who were diagnosed with COPD by a physician.However, those who had been diagnosed with lung cancer, bronchiectasis, pneumoconiosis, or other restrictive lung ventilation dysfunction were excluded from this study.
The sample size was calculated by the standard formula for a cross-sectional study 24 , n = [Z 2 α/2 PQ]/e 2 , where Z = the value of the standard normal distribution corresponding to the desired confidence level ( Z = 1.96 for 95% CI); P is the prevalence of good QOL among COPD patients in China at 14.1%, which was 0.14 25 ; Q is the difference of one and P (1-P); and e is the desired precision (0.05 or 5%).Allowing for 15% error throughout the study process, at least 213 individuals were required for the analysis.
After the sample size was calculated, six tertiary hospitals were randomly selected from among 108 hospitals by a computer-generated randomization method, as shown in the following flowchart (Fig. 1).To ensure that each sample site had an equal probability of providing a sample, simple random sampling with a proportional allocation of 0.25% was used to select the sample at each study site.Those who were selected were screened according to the inclusion and exclusion criteria before the initiation of data collection.

Research instruments
A validated questionnaire and the standardized SGRQ 26 were used for data collection.The validated questionnaire was developed according to the relevant literature and guidelines and discussed with experts in the field.The questionnaire consisted of three parts: general information about the participants, environmental factors, and the stage and treatment of COPD.In part one, twelve questions were used to collect general information about the participants, such as age, sex, marital status, educational level, occupational status, and household income.In part two, five questions were used to collect information on environmental factors such as residence, distance to the hospital, and hospital transport method.In the last part, five questions were used to collect information on the COPD stage and treatment of the participants.
The standardized SGRQ 26 was used to assess QOL among the participants.The SGRQ contains 50 items for assessing QOL in 3 domains: symptoms, activity, and impact.Each questionnaire response has a unique empirically derived 'weight' 26 .SGRQ scores range from "0" to "100", and "0" represents the best QOL.Finally, the participants were divided into three levels of QOL according to their scores: poor (scores of 66.68-100.00),

Data collection procedure
Six tertiary hospitals from among 108 hospitals with respiratory departments listed by the Ministry of Health and Population were randomly selected by a computer-generated randomization method and divided into two categories: tertiary class A hospitals and tertiary class B hospitals.Permission to assess the hospital was granted by the department director after sending official letters.The respiratory department staff were contacted to explain the purpose and questionnaire again to obtain their agreement to collect data in both outpatient and inpatient departments.
The purpose of this study and the content of the questionnaire were explained to the selected participants.Afterward, a written informed consent form was signed before starting data collection.The questionnaires

Statistical analysis
Data were entered into the spreadsheet and checked for any errors before being imported into the SPSS program (Version 24, Chicago, IL).Continuous data were analyzed and are presented as frequencies, means, maximums, minimums, and standard deviations to describe the participants' characteristics.Categorical data are presented as percentages.QOL was divided into three levels: low, moderate, and high.A chi-square test and Fisher's exact test were used to preliminarily test the associations between factors and good QOL.Logistic regression was used to determine the associations of factors and good QOL at a significance level α = 0.05 in both univariate and multivariate analyses.In the multivariate analysis, all predicted variables were entered into the model before non-statistical variable(s) were considered to exclude from the model.In this step, one most non-statistical variable was excluded from the model first, and considered the fit of the model by using the Hosmer-Lemeshow chi-square test before excluding the remaining non-statistical variable(s) in the model.The Cox-Snell R 2 and Nagelkerke R 2 were used to determine the fitness of the model before interpreting the final model.

Ethics approval and consent to participate
Ethical approval was obtained from Mae Fah Luang University (No. EC 21073-18).Participants were recruited on a voluntary basis.On the date of data collection, each participant received all the necessary information about the study protocol, the purpose of the survey and the potential risks.Participants were asked to sign consent forms before starting the interview.The study procedures were performed in accordance with the relevant guidelines, regulations, and within the Declaration of Helsinki of 1975, as revised in 2000 (5).

Results
A total of 420 COPD patients were recruited into this analysis: 56.4% were males, 48.1% were aged 70 years and over, and 67.1% were married.Approximately one-fifth (21.2%) were illiterate, 73.3% were unemployed, and 57.9% had an annual family income of less than 100,000 CNY ($14,750).Approximately twenty percent of participants (19.2%) faced problems with medical expenses, 69.8.0% self-paid for medical expenses, 73.3% had comorbidities, and 18.3% were current smokers (Table 1).
Nearly half of the participants (47.6%) lived in rural areas, and 48.3% went to a hospital by themselves.Half of the participants (43.8.0%) lived with others, and 40.5% had experienced exposure to secondhand smoke (Table 2).
Almost half (49.5%) had severe airflow limitation.A large proportion (61.9%) were reported to have been diagnosed with COPD for 60 months or more, 44.8% did not have home oxygen therapy available, and 49% had been hospitalized at least once in the past three months.A large proportion (62.9%) had visited their doctor 5 times or more in the last three months.Only one-fourth (25.7%) of the participants had good QOL (Table 3).
In the univariable analysis, 16 variables were found to be associated with good QOL: age, annual family income, cost of COPD treatment, BMI, medical insurance, number of comorbidities and types of comorbidities, such as hypertension, diabetes, and osteoporosis, current cigarette smoking, duration of smoking, distance from residence to hospital, exposure to secondhand smoke, airflow limitation severity, duration of illness, home oxygen therapy, number of hospitalizations within the past 3 months and doctor visits within the past 3 months.Other variables were not found to be associated with QOL (Table 4).
In the multivariable analysis, six variables were found to be associated with good QOL.Patients who were employed had 2.35 times (95% CI 1.03-5.34)greater odds of having good QOL than those who were unemployed.Those whose family income was higher than 1,00,000 CNY had 2.49 times (95% CI 1.15-5.39)greater odds of having good QOL than those whose family income was lower than 1,00,000 CNY.Those who had treatment expenses of less than 5000 CNY had 4.57 times (95% CI 1.57-13.30)greater odds of having good QOL than those who had treatment expenses of 5000 CNY or higher.Those who had mild or moderate airflow limitation had 5.27 times (95% CI 1.61-17.26)greater odds of having good QOL than those who had severe or very severe airflow limitation.Those who had a duration of illness less than 60 months had 5.57 times (95% CI 1.40-22.12)greater odds of having good QOL than those who had a duration of illness of 120 months or more.Those who had not been hospitalized within the past 3 months had 9.39 times (95% CI 1.62-54.43)greater odds of having good QOL than those who were hospitalized more than twice over the past 3 months (Table 4).

Discussion
Only one-third (24.8%) of the COPD patients who lived in Zhejiang Province, Chinn had poor QOL.Several factors were detected as contributors to having good QOL among COPD including employment status, high income, having been charged low treatment fees, having mild and moderated airflow limitation, having been diagnosed with COPD less than 60 months, and having never been admitted in a hospital.
The majority of people living in Zhejiang Province, China, had an annual family income of $14,750, which was higher than that of people living in other regions of China.COPD patients living in Shandong Province, where people had an annual family income lower than that in Zhejiang, had a lower proportion of good QOL 25,31 .Those people who lived in higher-income areas had higher levels of health insurance coverage, which supported them in accessing medical care and having better QOL than those who lived in poorer areas and had lower levels of health insurance coverage 25,31 .This finding confirmed that COPD patients living in high-income areas have www.nature.com/scientificreports/better QOL.This means that those who have a higher income would have a better opportunity for early diagnosis, treatment, and continuous care.Once carefully and continuously cared for, patients would have better QOL and less opportunity to be hospitalized due to poor management of the disease.Moreover, we found that COPD patients who were employed had better QOL than those who were not employed.Kupcewicz et al. 32 reported that COPD patients who were employed had better QOL than those who were retired.However, a large proportion of COPD patients were not actively working 33,34 .Due to its pathogenesis, the disease and the burden of medical expenses could be key impact factors of QOL as well 33 .
Even in our study, smoking was not found to be associated with QOL among COPD patients.However, many studies [35][36][37] have reported that smoking is a key factor of poor QOL among COPD patients.Smoking was reported as a significant risk factor for hospitalization among COPD patients 38,39 , especially among COPD patients with poor economic status 39 .A study in Korea 40,41 reported that COPD patients with a low family income had a greater chance of using cigarettes and had poorer QOL.This could reflect that COPD patients with a poor economic status have a greater chance of stress and start smoking, followed by a severe stage of COPD and low QOL.
Medical expenses or the cost of treatment was a significant factor associated with QOL among COPD patients living in Zhejiang Province, China.Medications account for the highest proportion of total medical costs for COPD patients 42,43 .Zhu et al. 14 and Li et al. 44 reported that a high medical cost was a direct factor in reducing QOL among COPD patients.Unaffordable medical costs of COPD patients were associated with a poor stage of COPD and poor QOL 14 .Basically, COPD patients need to attend a hospital regularly to check their health and obtain medications throughout their lives.If a patient cannot pay for medication, they enter a poor stage of the disease and have difficulty breathing, which directly impacts their QOL.Thus, affordable medical care is a significant factor in good QOL among COPD patients.
Our study clearly showed that the severity of airflow limitation among COPD patients was associated with their QOL.It is well known that impairment of lung function leads to a reduction in patients' ability to carry out daily activities 2,45 .COPD patients with severe airflow limitation often experience dyspnea, cough, fatigue, and declining lung function 46,47 .This affects their participation in social activities, including the limitation of occupational opportunities and interactions with their family members and other social activities.This could develop the individual's perception of being a burden to others because they need assistance to complete daily activities and finally manifest as impaired QOL 48 .Several studies 49,50 reported that COPD patients had poor QOL due to personal perceptions of their family members' burden, especially in the mental health domain.
We found that a longer course of disease led to a poorer level of QOL among COPD patients.On the other hand, those who had a shorter period of COPD development had better QOL than those who had a longer COPD diagnosis.Jankowska-Polańska et al. 51 also reported that COPD patients who lived for a shorter duration with the disease had a better QOL than those who had lived longer with the disease.Divo et al. 50reported that COPD patients who had lived with the disease longer had a greater opportunity to have a heavy cough in daily life than those who had lived with COPD for a shorter time.The study 52 also reported that coughing was a major sign associated with the QOL of COPD patients.Patients diagnosed over a longer period had a greater chance of being hospitalized than those diagnosed over a shorter period 52 .Several studies [53][54][55][56] reported that COPD patients who had been hospitalized presented panic or mental health problems compared with those who did not, eventually resulting in poorer QOL.Patients with longer illness could face a severe decline in mental health due to the stage of pathogenesis, lack of social interaction, and poorer self-confidence, resulting in poor QOL.
A greater number of hospitalizations indicated disease severity and patients with repeated admissions had significantly reduced QOL.Many studies [57][58][59] reported that COPD patients who had been hospitalized had poorer QOL.Physical, psychological, and social life impacts were detected among COPD patients who were frequently admitted to a hospital [60][61][62] , which directly impacted QOL.Some studies showed that patients with frequent exacerbations had a significantly lower QOL than patients with less frequent exacerbations 63 .Bernhard et al. 64 reported that changes in HRQOL were more dependent on the frequency of exacerbation than on FEV1 and DLCO decline.Hospitalization also increased the financial burden and reduced QOL 65 .Hospitalization among COPD patients could reduce their QOL due to physical, psychological, social life, and economic reasons.Some limitations were found in this study that could impact the results and interpretations.First, with the nature of a cross-sectional study that assesses both exposures and outcomes at the same time, quality of life might not be the exact consequence of the preceding factors.Good QOL among individuals might be the integrated outcome of many factors, especially living environment and family relations, which were not measured in our study.Second, the size of the study sample obtained from the standard formula for a cross-sectional study might impact the generalizability of the results to the general population.Last, using telephone calls to collect data might impact the completeness of the data and the quality of the data because physical body language could not be evaluated.

Conclusion
A large proportion of COPD patients living in Zhejiang Province, China, suffer from poor QOL.Several personal traits and the unaffordable cost of treatment are the major factors contributing to poor QOL among COPD patients.To improve QOL among COPD patients, public health policy-makers must develop a proper channel to increase accessibility to health care services, including affordable health insurance.Health institutes must consider supportive ways to provide medical services for COPD patients.Implementing measures to help COPD patients obtain a better job and higher income for family members is one of the challenges to ensure that COPD patients will be able to access medical care and have good QOL.
Flow of the study samples selection from six selected hospitals.